By means of standard electrophysiological methods, including constant-current and voltage-clamp techniques, the actions of chiriquitoxin and other analogues of tetrodotoxin will be studied on a variety of excitable membranes including the frog skeletal muscle fiber and several well-studied axons. The objective is the further understanding of the mechanism of interaction of tetrodotoxin and related compounds with the reciprocal membrane receptor, and to estimate the density and spatial relations of some of the major ionic conductance channels in the membranes.